Fat (also known as adipose tissue) is found in many parts of our bodies.
There is some fat stored in the liver and some fat over the kidneys. Subcutaneous fat is the fat stored below the skin, while visceral fat is the fat that lies deep in the abdomen between the organs. The distribution of fat in the body differs according to gender.
Fat cells are formed in a fetus during the third trimester of pregnancy. Throughout adult life, the number of fat cells remains the same. However, when we gain weight, the size of the fat cells increases.
Fat cells are known as adipose cells. They have many functions. The fat cells under the skin insulate the body and keep it warm. Fats act as cushion surrounding vital body organs. They also help the body store fat-soluble vitamins such as vitamins A, D, E and K. Fats also store energy and act as messengers that enable proteins to do their physiological roles.
There are two types of fat cells: white fat and brown fat.
White fat cells contain one large fat droplet and have fewer mitochondria and blood vessels. That is why they have a white or yellowish appearance. It is the most common fat in the body and it originates from connective tissue. We have a lot of white fat. White fat increases the risk of heart diseases, type-2 diabetes, and cancer. Overeating leads to increasing white fat.
Brown fat cells consist of several small fat droplets, several iron-containing mitochondria, and tiny blood vessels. The brown appearance is due to their iron content and blood vessels. Brown fat is found in the upper back and in the neck. This fat burns energy due to the high content of mitochondria and thus releases heat. Everyone has some brown fat.
It is suggested to promote the brown fat in the body since it helps us burn calories. It is recommended to eat apples often and to exercise regularly to promote the conversion of white fat to brown fat. Also, lower temperatures were found to cause white fat conversion to brown fat. Younger people have more brown fat than older individuals. And those with lower BMI were found to have more brown fat than those with high BMI.
Fat enters our bodies when we eat dietary fats. It passes through the stomach to the small intestine where it mixes with bile salts from the gall bladder and pancreatic juice. The bile salts cause emulsification of the fats – that is breaking the large fat droplets into smaller ones. The pancreatic juice contains lipase that breaks down fat into fatty acids and glycerol.
All this facilitates fat absorption in the small intestine. Inside the cells of the small intestine, the fat binds with a coating of protein forming chylomicrons. The protein part makes chylomicrons more water soluble. These chylomicrons are then released in the lymphatic system which in turn merges with veins releasing them into the blood stream.
People usually gain weight due to an imbalance between the food they consume and the calories they burn. If we eat excessively, we will store more calories and put on weight. Therefore in order to lose weight, we should eat a healthy diet. A diet of around 2000 calories is sufficient per day. We should also exercise regularly to burn calories.
However as we lose weight, the number of fat cells in our bodies will remain the same, but the cells will only get smaller in size. When we burn more calories than our consumption, the body stimulates the fat cells to release their stored fat content. Thus free fatty acids are released to the blood stream to reach the tissues that need the most energy.